Method for making readily defibered pulp product

ABSTRACT

A wet-laid wood pulp product containing cellulose pulp fibers and elongate precipitated calcium carbonate having a diameter of 0.015 to 0.6 microns at its maximum diameter and a length of 1 to 10 microns and the calcium carbonate being incorporated within the sheet and a method for making the product.

CROSS-REFERENCE TO RELATED APPLICATION

Related patent application includes U.S. patent application Ser. No.______ (Attorney Docket No. 26642), filed Dec. 31, 2008.

FIELD OF THE INVENTION

The invention is related to a wet-laid wood pulp product containingelongate sub-micron diameter precipitated calcium carbonate and a methodfor making it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are photomicrographs of an elongate sub-micron diameterprecipitated calcium carbonate.

FIGS. 3-6 are photomicrographs of cross sections of a pulp sheet showingthe location of the elongate sub-micron diameter precipitated calciumcarbonate in the pulp sheet.

FIG. 7 is a plot of fiberization (Kamas) energy for a control and theadditives.

FIG. 8 is a graph of fiberization (Kamas) energy vs. ash content of thepulps

FIG. 9 is a plot of dry bulk at 0.6 kPa for a control and for theadditives.

FIG. 10 is a plot of dry bulk at 2.5 kPa for a control and for theadditives.

FIG. 11 is a plot of wicking time for a control and for the additives.

FIG. 12 is a plot of wicking rate for a control and for the additives.

FIG. 13 is a plot of wet bulk at 2.5 kPa for a control and for theadditives.

FIG. 14 is a plot of resat bulk at 2.5 kPa for a control and for theadditives.

FIG. 15 is a plot of capacity for a control and for the additives.

DISCLOSURE

Fluff wood pulps are used as the absorbent layer in disposable diapers,sanitary napkins, and similar absorbent hygienic products. The cellulosepulp of the invention may be made using conventional kraft, sulfite,chemithermomechanical or other well known processes. The furnish can befrom any of various cellulose containing raw materials. Most usuallythese will be deciduous hardwoods, coniferous species, usually termedsoftwoods; or mixtures of these materials. A preferred pulp is ableached softwood kraft pulp that would normally be intended forultimate use as absorbent fluff.

Chemical pulp is prepared by chemically treating cellulosic materials,such as softwoods and hardwoods, to remove their lignin fraction andproduce a cellulosic pulp suitable for making paper and relatednon-woven products. Foremost among the chemical processes are thewell-known Kraft and sulfite pulping processes. In the Kraft pulpingprocess, a cellulosic source such as wood chips is digested with analkaline pulping liquor containing sodium hydroxide and sodium sulfide;while the sulfite process, as the name implies, employs a sulfurous acidsolution of an alkali or alkaline earth metal sulfite to effect ligninremoval. All known processes also generally rely on some type ofpost-digestion bleaching to obtain additional lignin removal, andincrease the whiteness and brightness of the pulp to enhance commercialacceptance

After the wood chips are digested and the resultant fibers bleached, thefibers are formed into a wet-laid pulp mat. In this operation, thefibers enter a headbox where they are mixed with water and any chemicalsthat need to be added to the pulp. The fibers exit the headbox onto amoving screen, known as a wire through which the water in the web isdrained both by gravity and by vacuum. This step, known in its initialstage as formation, is usually accomplished by passing an aqueousdispersion of a low concentration of pulp (e.g., 0.5% to 1% by weightsolids is typical) over the wire. This wire, assisted in certainsituations by vacuum or suction, increases the consistency of the mat orweb to approximately 20 to 35 weight percent solids.

The mat or web is then compressed or squeezed in a “press section” toremove additional water. This is usually accomplished by felt presses, aseries of rollers each having a felted band for contact with the mat orweb. These presses remove additional free water and some capillarywater, thus resulting in an increase in consistency of the mat or web toa range of about 30 to 60 weight percent. As is well known, in makingfluff pulp sheet, less pressure is applied in this portion of theprocess than normally would be encountered in conventional paper-making,thus less water is removed in this section. Less pressing is done so asto facilitate subsequent comminution of the fluff pulp sheet to thedefibrated fluffed pulp.

Following the press section, the pulp sheet is then dried in a dryersection. Because a reduced amount of water was removed in the presssection, more moisture must be removed from the sheet in the dryersection than generally is necessary in paper-making. In the driersection, the remaining water content of the pulp sheet is reduced toobtain a pulp consistency which typically ranges between about 88 to 97weight percent (3 to 12 weight percent moisture), more usually between90 to 94 weight percent (6 to 10 weight percent moisture). The wet-laidcellulose pulp fibers form into a sheet and attach to each other atcontact points by hydrogen bonds. This process is called wet forming.

In the United States it is most typically a fully bleached southern pinekraft process pulp produced in relatively heavy caliper, high basisweight sheets. The product is rewound into continuous rolls for shipmentto the customer. Since the rolls of product are intended to be laterreprocessed into individual fibers, low sheet strength is desirable andtypically little or no refining is used prior to sheeting. Therequirements for surface uniformity and formation are similarlymoderate.

Absorbent products are formed by dry-fiber air-laid techniques. The pulprolls are broken into dry fibers which are then conveyed by to a formingstation where they are formed into the absorbent product. The pulp rollis broken into individual fibers by disintegrating or comminutingdevices such as hammer mills. The energy required for disintegrating thepulp roll into individual fibers is large and a major expense of anabsorbent product plant.

In the absorbent product the pulp fibers serve as wicking agents to wickliquid away from the point of insult to other areas of the diaper andalso to absorb some of the liquid.

The present invention is a cellulosic wet-laid fluff pulp producttreated with elongate sub-micron diameter precipitated calcium carbonateand the method of its manufacture. The product can be converted fromsheeted or roll form into individual fibers with significantly reducedfiberization energy input and the fibers in the air-laid product havewicking similar to untreated fibers and have good drape as shown byGurley stiffness.

The pulp products of the present invention are clearly differentiatedfrom products intended as letter, book, magazine, or similar papers. Thecaliper of a pulp sheet is 0.02 to 0.08 inches (0.051 to 0.203 cm). Thebasis weight of the products of the present invention may be as low asabout 200 g/m² to 1000 g/m². The fiber will most usually be unrefined oronly lightly refined although the invention is not so limited. Where ahigh surface area product is desired the fiber will normally besignificantly refined. The pulp products are unsized is such as toclearly distinguish them from ordinary papers which might contain highamounts of sizing agents. The products of the present invention areunsized and the strength properties such as tensile, burst, and tearstrength, which are considered essential in papers, are generally muchlower. Pulp is normally not used in its roll form. It is disintegratedback to fibers, either by a disintegrating device such as a hammer mill,if the fibers are to be air laid, or in a broke tank with water if thefibers are to be wet-laid into paper.

Pulp used for papermaking is usually relatively highly refined todevelop web strength. The caliper of a paper sheet is 0.003-0.0175inches (0.002-0.045 cm). The basis weight of paper is normally based on500 sheets of paper at the standard uncut size for that type of paper.These have been converted to grammage. To compare a pulp sheet and apaper sheet the basis weight of paper has for this purpose beenconverted to the basis weight of a single sheet of paper. The basisweight of a single sheet of paper is 0.072 to 0.976 g/m². Good strengthis essential. Papers are normally sized to improve ink holdout and otherprinting properties.

The cellulose pulp of the invention may be made using conventionalkraft, sulfite, chemithermomechanical or other well known processes. Thefurnish can be from any of various cellulose containing raw materials.Most usually these will be deciduous hardwoods, coniferous species,usually termed softwoods; or mixtures of these materials. A preferredpulp is a bleached softwood kraft pulp that would normally be intendedfor ultimate use as absorbent fluff. While so-called “dissolving pulps”may be used these are not preferred because of their low yield andresultant much greater cost. Never-dried or once-dried may be used toform the wet-laid sheet of pulp.

In the present application elongate sub-micron diameter precipitatedcalcium carbonate is added to the slurry of cellulose pulp fibers in theheadbox and is combined with the pulp in the pulp sheet during itsformation and drying so that the calcium carbonate is incorporated intothe wet-laid pulp sheet.

Normally retention aids such as Nalco 71708 and similar products arerequired to attach calcium carbonate or other materials to cellulosepulp fibers. No retention aid is needed for the attachment of theelongate sub-micron diameter precipitated calcium carbonate to thefibers. The calcium carbonate attaches directly to the fibers.

The calcium carbonate is elongate sub-micron diameter precipitatedcalcium carbonate. It has a diameter at its maximum diameter of 0.015 to0.6 micron. In one embodiment it has a diameter at its maximum diameterof 0.015 microns to 0.06 micron. In another embodiment it has a diameterat is maximum diameter of 0.2 to 0.45 micron. In another embodiment ithas a diameter at is maximum diameter of 0.15 to 0.25 microns. In oneembodiment it has a length of 1 to 10 microns. Its diameter may varyalong its length and it may be narrower at its ends than it is at apoint between its ends. Elongate sub-micron diameter precipitatedcalcium carbonate may be in three forms, a short form having a length of1 to 3 microns, and medium form having a length of 3 to 6 microns, and along form having a length of 6 to 10 microns. The short form usuallyaverages 2 microns in length and the medium form usually averages 4microns in length, and the long form usually average 8 microns inlength. Each of these forms may have any of the diameters noted above.

Several companies provide the elongate sub-micron diameter precipitatedcalcium carbonate. NanoMaterials Technology Pte Ltd (NMT) provides anelongate precipitated calcium carbonate made using the high gravityreactive precipitation (HGRP) technology platform. It has a diameter of0.015 to 0.06 micron at its largest diameter with an average diameter atits largest diameter of 0.045 micron.

Solvay, S. A. provides an elongate precipitated calcium carbonate thathas a diameter of 0.25 to 0.45 micron at its largest diameter with anaverage diameter at its largest diameter of 035 micron. It is sold underSOCAL® 90A, NZ or P2E. It has an aragonite crystal form and isortho-rhombic. Solvay, S. A. also provides another elongate precipitatedcalcium carbonate that has a diameter of 0.15 to 0.25 micron at itslargest diameter with an average diameter at its largest diameter of 0.2micron. It is sold under SOCAL® P1V, P2, P2V, P3E, 93V, 94V, NP, N2, N2Ror P2PHV. It has a calcite crystal form and is scalenohedral.

Elongate sub-micron diameter precipitated calcium carbonate is shown inFIGS. 1 and 2. The magnification in FIG. 1 is 2000 times; themagnification in FIG. 2 is 10,000 times.

For the purposes of this application sub-micron diameter precipitatedcalcium carbonate is precipitated calcium carbonate 0.015 to 0.6 micronin diameter at its maximum diameter and 1 to 10 microns in length. Anembodiment of the sub-micron diameter precipitated calcium carbonate hasa diameter at its maximum diameter of 0.015 to 0.45 micron. Anotherembodiment of the sub-micron diameter precipitated calcium carbonate hasa diameter at its maximum diameter of 0.015 to 0.35 micron. Anembodiment of the sub-micron diameter precipitated calcium carbonate hasa length of 1 to 3 microns. Another embodiment of the sub-microndiameter precipitated calcium carbonate has a length of 3 to 6 microns.Another embodiment of the sub-micron diameter precipitated calciumcarbonate has a length of 3 to 10 microns.

The elongate sub-micron diameter precipitated calcium carbonate is addedto the slurry in the headbox with any other chemicals prior to theformation of the mat. Consequently the sub-micron diameter precipitatedcalcium carbonate is throughout the mat. This can be seen in FIGS. 3through 6 which are cross sections of the pulp sheet. The sub-microndiameter precipitated calcium carbonate is white and remains elongate.

The amount of elongate sub-micron diameter precipitated calciumcarbonate added to the pulp may be from 3 to 45% of the dry weight ofthe pulp.

The purpose of the elongate sub-micron diameter precipitated calciumcarbonate is to provide a sheet that requires less fiberization energythan a pulp without the elongate sub-micron diameter precipitatedcalcium carbonate or other similar fiberization agent when the pulpsheet is comminuted and to provide wicking that is the same or close tothe wicking of an absorbent product as a pulp without the elongatesub-micron diameter precipitated calcium carbonate. Although retentionaids may be used if desired there is no need to use retention aid whenusing sub-micron diameter precipitated calcium carbonate.

The energy required to defiberize the pulp sheet may be reduced by asmuch as 30% from a pulp without sub-micron diameter precipitated calciumcarbonate or similar fiberization agent when a target of 5% by weight ofa elongated sub-micron diameter precipitated calcium carbonate is mixedin the pulp sheet. The decrease may be as much as 50% from a pulpwithout sub-micron diameter precipitated calcium carbonate or similarfiberization agent when a target of 10% by weight of elongate sub-microndiameter precipitated calcium carbonate is mixed in the pulp sheet.

The elongate sub-micron diameter precipitated calcium carbonate hasbetter fiberization characteristics than a cubic shaped nanoprecipitated calcium carbonate. The cubic shaped nano precipitatedcalcium carbonate has substantially the same fiberization energy as apulp that does not have any cubic or elongate sub-micron diameterprecipitated calcium carbonate.

The addition of elongate sub-micron diameter precipitated calciumcarbonate reduces the Gurley stiffness. An addition of a target of 10%by weight of the weight of the pulp reduces the Gurley stiffness byaround 25%. An addition of a target of 40% by weight of the weight ofthe pulp reduces the Gurley stiffness by around 83%.

The shape of the elongate sub-micron diameter precipitated calciumcarbonate does not appear to matter. The examples show the wicking andfiberization energy characteristics to be similar.

In the method of making the wet laid cellulose pulp sheet the cellulosepulp fibers and elongate sub-micron precipitated calcium carbonate areadded to a headbox. The cellulose pulp fibers and elongate sub-micronprecipitated calcium carbonate may be mixed before being added to theheadbox or may be mixed in the headbox. In one embodiment the amount ofelongate sub-micron precipitated calcium carbonate is 3 to 45 percent ofthe weight of the cellulose pulp fiber. In another embodiment the amountof elongate sub-micron precipitated calcium carbonate is 3 to 15 percentof the weight of the cellulose pulp fiber. Retention aid need not beadded though it can be added if desired. The mixture is placed on a wireand the water is pulled from the sheet by vacuum, forming a wet sheetcomprising the cellulose pulp fibers and the elongate sub-micronprecipitated calcium carbonate. The elongate sub-micron precipitatedcalcium carbonate is incorporated within the sheet among the cellulosefibers. It has been found that the elongate sub-micron precipitatedcalcium carbonate attaches to the fibers without the need for retentionaid. The wet-laid sheet is usually pressed to remove more water and isthen dried. The sheet usually contains from 6 to 12% water.

In the examples that follow:

Fiberization energy requirement is determined using a laboratory scalehammermill instrumented to measure power necessary to fiberize a givenweight of pulp. The mill used in the following tests was a KamasLaboratory Mill, Model H01, manufactured by Kamas Industri, AB,Vellinge, Sweden. The breaker bar clearance of the mill was set at 4.0mm, the screen size was 19 mm, and rotor speed was adjusted to 3024 rpm.Samples were conditioned at 50% R.H. for a minimum of 4 hours prior totesting. The samples were cut into strips 5.0 cm wide and as long as thesample would permit. Sufficient strips were cut to yield about 150 g offiberized pulp. Basis weight of the samples was previously determinedand the hammermill feed roller speed was adjusted to achieve a targetfeed rate of 2.80 g/sec

Water absorption rate was determined by using the automatic fluffabsorption quality (FAQ) test. The fluff is first formed into an airformed pad within a cylinder 16 cm long and 5.7 cm in diameter having awire screen at the bottom. The tared cylinder is placed on a balance andpad weight adjusted to 4.0 g by carefully removing any excess fiber fromthe top with tweezers. The pad height is measured under a no-loadcondition and the dry bulk under no load is calculated. A 2.5 kPapressure is applied to the pad, the pad height is again measured and thedry bulk under load is calculated. The bulk is calculated as cubiccentimeters per 1 gram. The pad within the cylinder is then placed inthe tester and a 2.5 kPa pressure is applied. This is done by lowering a150 g plunger onto the fluff mat. Water is then introduced at the baseof the pad so that the water just touches the screen at the bottom ofthe pad. Wicking time is the time it takes water to wick through fromthe bottom of the loaded pad to the top of the loaded pad. The height ofthe wetted pad is then measured. The wicking rate is the wicking timedivided by the average of the loaded dry bulk height and the loaded wetbulk height [(loaded dry bulk height +loaded wet bulk height)/2], and isreported in mm/second. The load is then removed and the fluff is allowedto absorb as much water as possible in the no-load condition (60s).No-load (Resat) wet height/bulk is then measured. The Plexiglas tubecontaining wet fluff is moved to a balance and weighed to calculate howmuch water was absorbed. The dry tube tare weight is included in thecalculation. The fluff pad initially weighed 4 g dry, but absorptioncapacity is reported as gram of water/gram of fluff.

The pulp used in the examples in this application is a bleached southernpine kraft wood pulp from southeastern U.S. pulp mills. This grade isproduced as a market fluff pulp. The NB-416 grade is sold byWeyerhaeuser Company from its New Bern, North Carolina mill. The CF-416grade is sold by Weyerhaeuser Company from its Columbus, Miss. mill.This grade is produced as a market fluff pulp and was used both as acontrol material and as a base material in all of the examples in theapplication. The elongate sub-micron diameter precipitated calciumcarbonate or other additive was added to and mixed with the pulp priorto making the handsheet. In the following examples, a target means thatamount was targeted for addition but the actual amount added wasapproximately the targeted amount. For example a target of 5% meansapproximately 5% was added.

EXAMPLE 1

Hand sheets were made on a 12″ by 12″ handsheet former using once driedNB 416 pulp at a targeted basis weight of 750 g/m². The results of thecomparison are shown in Table 1. In column 1, the control was once driedonce dried NB 416 pulp. In column 2, a target of 5% elongate sub-microndiameter precipitated calcium carbonate from NanoMaterials Technologyhaving a mean length of 4 microns was added to the once dried NB 416pulp. In column 3, a target of 10% elongate sub-micron diameterprecipitated calcium carbonate from NanoMaterials Technology have a meanlength of 4 microns was added to the once dried NB 416 pulp. In column4, a target of 5% cubic shaped precipitated calcium carbonate have amean length of 4 microns was added to the once dried NB 416 pulp. Incolumn 5, a target of 10% cubic shaped precipitated calcium carbonatehave a mean length of 4 microns was added to the once dried NB 416 pulp.The amount of calcium carbonate added was based on the total weight ofthe sheet. No retention aid was used.

TABLE 1 1 2 3 4 5 Basis weight g/m² 813 811 825 811 789 Caliper mm 1.531.55 1.63 1.54 1.51 Density Kg/m² 530 522 505 526 524 Formationvariability % 6.6 4.9 3.4 6.3 7.8 Energy required kJ/kg 76 54 40 76 75Energy reduction % 29 47 — — Fluff dry bulk 0.6 kPa 51.3 51.1 46.3 52.452.7 cc/g Fluff dry bulk 2.5 kPa 24.7 25.2 23.6 25.9 25.8 cc/g Wicktime, seconds 2.1 2.1 2.1 2.2 2.3 Wicking rate mm/sec. 12.9 12.8 12.512.7 12.2 Fluff wet bulk 2.5 kPa 9.6 9.2 8.9 9.7 9.6 cc/g Fluff wet bulk0.6 kPa 10.7 10.2 9.9 10.7 10.6 cc/g Capacity g/g 10.4 9.8 9.2 10.4 10.3

It can be seen that the fiberization energy in columns 2 and 3 are farless than those in columns 1, 4 and 5 while the fiberization energy incolumns 4 and 5 are about the same as the control in column 1. Thewicking times and wicking rates in all of the columns are about thesame.

EXAMPLE 2

The fiberization energy of pulp containing elongate sub-micron diameterprecipitated calcium carbonate, whether from NanoMaterials Technology orSOCAL from Solvay, S A., is far less than either a control pulp sheetwithout additives. At the same addition rate the NanoMaterialsTechnology and SOCAL elongate sub-micron diameter precipitated calciumcarbonate had the same fiberization energy. The wicking times or wickingrates of pulp containing elongate sub-micron diameter precipitatedcalcium carbonate were slightly greater than the control pulp sheet. Theshape of the elongate sub-micron diameter precipitated calcium carbonatedid not matter. This is shown in Table 2.

Hand sheets were made on a 12″ by 12″ handsheet former using once driedCF 416 pulp at a targeted basis weight of 750 g/m². Table 2 shows theresults. In column 1, the control was once dried CF 416 pulp. In column2, a target of 10% elongate sub-micron diameter precipitated calciumcarbonate from NanoMaterials Technology having a mean length of 4microns was added to the once dried CF 416 pulp. In column 3, a targetof 10% elongate sub-micron diameter precipitated calcium carbonate(SOCAL 90) was added to the once dried CF 416 pulp. In column 4, atarget of 10% elongate sub-micron diameter precipitated calciumcarbonate (SOCAL 92) was added to the once dried CF 416 pulp. The amountof elongate sub-micron diameter precipitated calcium carbonate added wasbased on the total weight of the sheet.

TABLE 2 1 2 3 4 Basis weight g/m² 944 943 947 985 Caliper mm 1.58 1.581.60 1.59 Density Kg/m² 596 596 593 620 Formation variability % 8.3 7.66.4 7.1 Energy required kJ/kg 107 79 89 79 Energy reduction % 26 17 26Fluff dry bulk 0.6 kPa cc/g 54.6 47.8 48.5 47.9 Fluff dry bulk 2.5 kPa26.5 24.0 24.8 24.3 cc/g Wick time, seconds 2.2 1.8 1.9 1.8 Wicking ratemm/sec. 13.3 14.6 14.0 14.5 Fluff wet bulk 2.5 kPa 9.9 9.1 9.2 9.1 cc/gFluff wet bulk 0.6 kPa 11.1 10.1 10.3 10.3 cc/g Capacity g/g 10.9 9.79.8 10.0

EXAMPLE 3

The fiberization energy of once dried pulp containing elongatesub-micron diameter precipitated calcium carbonate is far less thaneither a control pulp sheet without additives or a pulp sheet containingother additives. This is shown in a comparison of elongate sub-microndiameter precipitated calcium carbonate and Tech 4, Tech 8 and Vansil 20at a target of 5% by weight addition to the once dried pulp.

Hand sheets were made on a 12″ by 12″ handsheet former using NB 416 pulpat a targeted basis weight of 750 g/m². The results of the comparisonare shown in Table 3. In column 1, the control was NB 416 pulp. Incolumn 2, a target of 5% elongate sub-micron diameter precipitatedcalcium carbonate having a mean length of 4 microns was added to theonce dried NB 416 pulp. In column 3, a target of 5% Tech 4 was added tothe once dried NB 416 pulp. In column 4, a target of 5% Tech 8 was addedto the once dried NB 416 pulp. In column 5, a target of 5% Vansil 20 wasadded to the once dried NB 416 pulp. The amount of elongate sub-microndiameter precipitated calcium carbonate or additive added was based onthe total weight of the sheet. It can be seen that the fiberizationenergy for the elongate sub-micron diameter precipitated calciumcarbonate was superior to the control or the samples with Tech 4, Tech 8or Vansil 20 pigments and the wicking rate for the elongate sub-microndiameter precipitated calcium carbonate is the same as for the pigments.

TABLE 3 1 2 3 4 5 Basis weight g/m² 758 782 771 788 791 Caliper mm 1.291.30 1.26 1.33 1.33 Density Kg/m² 590 601 611 592 594 Formationvariability % 5.9 7.7 4.4 6.4 6.0 Energy required kJ/kg 86 59 84 84 79Energy reduction % 31 2 2 8 Fluff dry bulk 0.6 kPa 50.9 51.0 53.2 51.650.7 cc/g Fluff dry bulk 2.5 kPa 25.7 25.9 26.3 25.5 25.2 cc/g Wicktime, seconds 2.5 2.1 2.0 2.0 2.1 Wicking rate mm/sec. 11.3 13.5 14.313.9 13.4 Fluff wet bulk 2.5 kPa 9.5 9.2 9.7 9.5 9.7 cc/g Fluff wet bulk0.6 kPa 10.7 10.2 10.8 10.7 10.7 cc/g Capacity g/g 10.6 10.0 10.5 10.210.5

EXAMPLE 4

The same additives as those used in Table 3 were also compared at a 10%weight addition. Hand sheets were made on a 12″ by 12″ handsheet formerusing once dried NB 416 pulp at a targeted basis weight of 750 g/m². Theresults of the comparison are shown in Table 4. In column 1, the controlwas once dried NB 416 pulp. In column 2, a target of 10% elongatesub-micron diameter precipitated calcium carbonate having a mean lengthof 4 μm was added to the once dried NB 416 pulp. In column 3, a targetof 10% Tech 4 was added to the once dried NB 416 pulp. In column 4, atarget of 10% Tech 8 was added to the once dried NB 416 pulp. In column5, a target of 10% Vansil 20 was added to the once dried NB 416 pulp.The amount of elongate sub-micron diameter precipitated calciumcarbonate or additive added was based on the total weight of the sheet.Again the fiberization energy of the elongate sub-micron diameterprecipitated calcium carbonate was far superior to the control or theadditives while the wicking rate of the elongate sub-micron diameterprecipitated calcium carbonate was comparable to the additives.

TABLE 4 1 2 3 4 5 Basis weight g/m² 758 837 816 843 830 Caliper mm 1.291.40 1.33 1.33 1.37 Density Kg/m² 590 599 612 634 606 Formationvariability % 5.9 6.4 3.8 7.0 7.1 Energy required kJ/kg 86 43 78 78 79Energy reduction % 50 9 9 9 Fluff dry bulk 0.6 kPa 50.9 45.7 51.8 49.650.6 cc/g Fluff dry bulk 2.5 kPa 25.7 23.3 26.1 25.2 25.0 cc/g Wicktime, seconds 2.5 1.9 2.0 2.1 2.2 Wicking rate mm/sec. 11.3 13.6 14.213.0 12.7 Fluff wet bulk 2.5 kPa 9.5 8.7 9.7 9.1 9.6 cc/g Fluff wet bulk0.6 kPa 10.7 9.6 10.7 10.2 10.6 cc/g Capacity g/g 10.6 9.1 10.4 9.9 10.4

As can be seen from the examples elongate sub-micron diameterprecipitated calcium carbonate greatly reduces the fiberization energyof a pulp sheet while maintaining the wicking performance of theresultant air-laid pad.

EXAMPLE 5

Samples were made using never dried NB 416 cellulose pulp fiber with (1)no sub-micron diameter precipitated calcium carbonate (control), with(2) SOCAL 90A (PCC1) sub-micron diameter precipitated calcium carbonateadded to the slurry at targets of 5% and 10% of the oven dry weight ofthe sheet, with (3) SOCAL P2 (PCC2) sub-micron diameter precipitatedcalcium carbonate added to the slurry at targets of 5% and 10% of theoven dry weight of the sheet, and with (4) NanoMaterials Technology(NMT) sub-micron diameter precipitated calcium carbonate (NPCC) added tothe slurry at targets of 5% and 10% of the oven dry weight of the sheet.No retention aid was used the sub-micron diameter precipitated calciumcarbonate. The results are given in Table 6 and 7 and in FIGS. 7-15. Theash content in FIG. 8 is the amount of elongate sub-micron diametercalcium carbonate retained on the sheet.

Table 5 shows the results of the 5% addition tests in which the targetamount of sub-micron diameter precipitated calcium carbonate is targetedat 5% of the weight of the sheet. Column I is the never dried NB 416pulp control; column 2 is a target of 5% PCC1 added to the never driedNB 416 pulp; column 3 is a target of 5% PCC2 added to the never dried NB416 pulp and column 4 is a target of 5% NPCC from NanoMaterialsTechnology added to never dried NB 416 pulp.

TABLE 5 1 2 3 4 Actual ash content, % 0.19 3.63 1.88 3.89 Energyrequired, kj/Kg 130.6 102.4 112.9 97.7 Energy reduction % 22 14 25 Drybulk 0.6 kPa, cc/g 53.7 50.6 51.4 51.8 Dry bulk 2.5 kPa, cc/g 27.6 26.126.2 27.1 Wick time, sec. 2.67 2.10 2.07 2.23 Wicking rate, mm/sec 11.313.4 13.8 13.0 Wet bulk 2.5 kPa 10.3 9.53 9.74 9.66 Resat bulk 11.3210.63 10.82 10.81 Capacity, g H₂O/g pulp 11.21 10.36 10.64 10.63

Table 6 shows the results in which the target amount of sub-microndiameter precipitated calcium carbonate is 10% of the weight of thesheet. Column 1 is the never dried NB 416 pulp control; column 2 is atarget of 10% PCC1 (12.5% of PCC1) added to the never dried NB 416 pulp;column 3 is a target of 10% PCC2 added to the never dried NB 416 pulpand column 4 is a target of 10% NPCC from NanoMaterials Technology addedto never dried NB 416 pulps.

The fiberization energy was greatly reduced with use of the elongatesub-micron diameter precipitated calcium carbonate was reduced from 25%to 42%. The wicking rate increased from 11.3 to 14.1 mm/sec.

TABLE 6 1 2 3 4 Actual ash content, % 0.19 6.02 1.88 3.89 Energyrequired, kJ/kg 130.6 85.0 97.4 75.1 Energy reduction % 35 25 42 Drybulk 0.6 kPa, cc/g 53.7 46.9 46.6 50.2 Dry bulk 2.5 kPa, cc/g 27.6 24.725.0 26.2 Wick time, sec. 2.67 2.03 1.93 2.00 Wicking rate, mm/sec 11.313.2 14.0 14.1 Wet bulk 2.5 kPa 10.3 9.13 9.28 9.38 Resat bulk 11.3210.25 10.33 10.50 Capacity, g H₂O/g pulp 11.21 9.87 10.17 10.18

EXAMPLE 6

Hand sheets were made on a 12″ by 12″ handsheet former using once-driedCF 416 pulp at a targeted basis weight of 100 g/m². The pulp was mixedin a British Disintegrator for 5 minutes. It was then diluted to about0.5% consistency. The pulp was then placed in the former and aircouched. The handsheet was pressed at 20 psi on a screen with top andbottom blotters. It was run through a Gess Press at 100 psi with top andbottom blotters, and dried in a drum dryer at 350° F. for 10 minutes oneach side. The sub-micron diameter precipitated calcium carbonate wasadded to the pulp after the pulp consistency was lowered and before thehand sheet formation. The combination mixed for one minute. The 4 micronaverage length sub-micron diameter precipitated calcium carbonate wasused at targeted 10% and 40% of the weight of the oven dried pulpaddition

The softness was measured using the TAPPI test method T543 of 94 forGurley stiffness.

Pulp test samples were 1 inch wide and 3½ inches long. The samples weretest with a 5 g weight 1 inch from the center.

The control 12 inch by 12 inch handsheet had 9 g of pulp. The controltest sample cut from the handsheet had a Gurley stiffness of 331.6 mg.

The first test 12 inch by 12 inch handsheet was targeted for thesub-micron diameter precipitated calcium carbonate being 5% of theweight of the pulp. The handsheet had 8.55 g of pulp and 0.45 g ofsubmicron precipitated calcium carbonate. The test sample cut from thehandsheet had a Gurley stiffness of 250.0 mg. There was a 25% decreasein Gurley stiffness.

The second test 12 inch by 12 inch handsheet was targeted for thesub-micron diameter precipitated calcium carbonate being 10% of theweight of the pulp. The handsheet had 8.1 g of pulp and 0.9 g ofsubmicron precipitated calcium carbonate. The test sample cut from thehandsheet had a Gurley stiffness of 90.0 mg. There was a 73% decrease inGurley stiffness.

The Gurley stiffness was substantially lower when sub-micron diameterprecipitated calcium carbonate was added to the pulp.

It will be understood that changes can be made without departing fromthe spirit of the invention.

1. A method of making a wet laid cellulose pulp sheet comprising providing cellulose pulp fibers to a headbox, providing elongate precipitated calcium carbonate having a diameter of 0.015 to 0.6 microns at its maximum diameter and a length of 1 to 10 microns to the headbox. forming a wet sheet comprising the cellulose pulp fibers and the elongate precipitated calcium carbonate, dewatering and drying the sheet to form a wet-laid pulp sheet incorporating within the sheet the elongate nano or near nano precipitated calcium carbonate.
 2. The method of claim 1 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 40% of the weight of the cellulose pulp.
 3. The method of claim 1 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 15% of the weight of the cellulose pulp.
 4. The method of claim 1 wherein the elongate precipitated calcium carbonate is 1 to 3 microns in length.
 5. The method of claim 1 wherein the elongate precipitated calcium carbonate is 3 to 10 microns in length.
 6. The method of claim 1 wherein the elongate precipitated calcium carbonate is 0.015 to 0.45 microns in diameter at its maximum diameter.
 7. The method of claim 6 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 40% of the weight of the cellulose pulp.
 8. The method of claim 6 wherein the elongate precipitated calcium carbonate is present in the amount of 3 to 15% of the weight of the cellulose pulp.
 9. The method of claim 6 wherein the elongate precipitated calcium carbonate is 1 to 3 microns in length.
 10. The method of claim 6 wherein the elongate precipitated calcium carbonate is 3 to 10 microns in length. 